XAS and XRD Structural Characterization of Lanthanum-Modified PbTiO₃ Ceramic Materials

Abstract

For the first time combined X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) experiments were carried out to probe the short- and long-range order in lanthanum-modified PbTiO3 ceramic materials (Pb1 - x La x TiO3) for x ranging from 0 to 30 atom % of La. XRD results show that a tetragonal structure fitted well to all samples, except to the one with 30 atom % of La for which XRD results highlighted a cubic unit cell. XRD refinements also confirmed the existence of only A-site vacancies. X-ray absorption near edge spectroscopy (XANES) measurements indicate that the local structure around Ti atoms has a different compositional dependence from the one obtained from XRD, mainly for the sample with 30 atom % of La. According to XANES data, for the sample with 30 atom % of La, a local distortion around Ti atoms persist. The analysis of extended X-ray absorption fine structure (EXAFS) spectra shows a decrease in the local disorder around Ti atoms as the content of La increases. Structural details, in terms of short and long-range order, are presented and the correlation between the XRD and XANES/EXAFS data is discussed.

Electronic structure of Pb1−xLaxTiO3 ferroelectric materials from Ti 2p and O 1s soft x-ray absorption spectroscopy

“…Earlier XRD studies on these compounds confirmed the existence of only Pb-site vacancies. 7 On the other hand, XAS studies show that the local structure of the titanium site is only slightly dependent on the crystallographic phase. 7 Thus, the changes observed in the e g states of Ti L 3,2 XANES spectra of the PLT samples, such as the amount of lanthanum increases found in this work, can be attributed primarily to the replacement of Pb atoms by La atoms and to the subsequent creation of vacancies on Pb site.…”

“…% using XAS and XRD techniques. 7 Our XRD results indicated that all our samples possessed a tetragonal structure except the one containing 30 at. % of La, which exhibited a cubic unit cell.…”

“…7,21 To maintain the neutrality of the charge, since that replacement is aliovalent, vacancies in the Pb site are created. Earlier XRD studies on these compounds confirmed the existence of only Pb-site vacancies.…”

“…Details of the samples' preparation are reported elsewhere. 7 Room temperature XANES measurements were taken on the spherical grating monochromator ͑SGM͒ beam line for Visible Ultraviolet ͑VUV͒ and soft x-ray spectroscopy of the Brazilian Synchrotron Light Source ͑LNLS͒, operating with an electron beam energy of 1.36 GeV and a current between 100-160 mA. The Ti L 3,2 edge ͑455-470 eV͒ and O K-edge ͑520-555 eV͒ XANES spectra were measured by collecting the total electron yield current from the samples with an energy resolution of around 0.5 eV.…”

“…% of La. 7 Although the use of x-ray absorption spectroscopy to study ABO 3 and mixed perovskite compounds has been limited mainly to the analysis of K-edge spectra, the electronic structure of the transition metals in these compounds has recently been studied by soft x-ray absorption spectroscopy measurements of Ti L 3,2 and O K edges. [8][9][10][11][12][13][14] When applied to mixed perovskite compounds, these studies proved very useful in shedding light on how compositional substitution influences the electronic structure of these systems.…”